MerCruiser 3.0 valve adjustment by the book 0 compression

[lr3guyjoe]

Ive had a slight valve click so I thought I would go ahead and attempt to adjust my valves while “ Social distancing”

I’m trying to do the valve adjustment on a 3.0 MerCruiser. I’m doing it by the book number one at TDC and adjusting intake and exhaust on the identified valves. Then turning over to TDC on number four and doing the associated exhaust and intake valves. I tighten the nut slightly until the push rod will not spin between my fingers then I tighten 3/4 of a turn.

After doing this I lose pretty much all compression on all of the cylinders... i’ve done it twice now with the same results. I’m totally lost.

I’m assuming I’m going to far because if I back off slightly compression comes back. The battery I’m using to turn over the engine is on a jump box is slightly weak. Not sure if the engine needs to spin over faster for the lifters to pump up?

Any suggestions on what I’m doing wrong?

 

[Alumarine]

You're over adjusting, easy to do. I have the tshirt.
When you're spinning the rod and you feel a bit of resistance then do the 3/4 turn.
Try that out.

 

[Rick Stephens]

Taking out the lash is not done spinning the rod but by wriggling the rod up and down until the slack is out.

 

[racerone]

Post #1 does not mention TDC on the compression / firing stroke.----Have done this job numerous times with engines running.-------I know , can get messy on a boat.

 

[Bondo]

Taking out the lash is not done spinning the rod but by wriggling the rod up and down until the slack is out.

Ayuh,..... Rick is dead on the money,.....

Forget about Spinnin' the push-rods, 'n gently move 'em up, down, til there is no more up, down, then 3/4 turn more,.....

That's the most deceivin' process in so many shop manuals, it ain't funny,.....

 

[muc]

Taking out the lash is not done spinning the rod but by wriggling the rod up and down until the slack is out.

I agree that some amateurs shouldn't try to use the spinning method, that might be best left to the pros.

But if you do want to try. You can take a look at MerCruiser manual #90-840283R01. On page 3A-19 you will find the instructions to the correct way.

4. Loosen adjusting nut until lash is felt at push rod, and then hand tighten adjusting nut
until all lash is removed. Lash can be checked by rotating push rod while hand tightening
adjusting nut until all play is removed.
IMPORTANT: If the lifter has not been pumped up with oil, the push rod could be rotated
while the plunger in the lifter is being collapsed. Any resistance felt while rotating
the push rod should be considered no lash. This can be checked by making sure
there is no up and down movement of the push rod or zero clearance between the
rocker arm and valve stem.

It's kind of like using feeler gauges. Once you have tried a .024', .025' .and a .026' in a shim tool that asks for .025' clearance. And you find that the .024 won't go in at all and the .026 is way loose, you now know what a feeler gauge should feel like when you slide that .025 in and out.


I do think that learning how to adjust valves by spinning the push rod is a skill worth having. It will allow you to do a more precise job faster.